The conventional single casing water meter as shown in FIG. 1 of the accompanying drawings consists of a water chamber 2 arranged in the lower portion of the meter casing, a vane wheel 3 mounted within said water chamber 2, an inlet port 1a and an outlet port 1b each integrally formed on both sides of, and substantially at a level with, said water chamber 2, wherein said inlet and outlet ports 1a and 1b directly communicate with said water chamber 2.
Therefore, in operation of such a single casing water meter, said vane wheel and the registering mechanism (not shown in the drawings) receives a sudden impact caused by a water hammer, whereby said vane wheel 3 rotates under the one-sided pressure applied from said inlet port 1a, so that the vane wheel shaft and bearing or pivot are subjected to one-sided abrasion, thus resulting in inaccurate measurement and shortening the instrument life.
In order to eliminate such disadvantages of the single casing water meter and to improve the rotational condition thereof, the conventional double casing water meter as shown in FIG. 2 of the accompanying drawings has been constructed in such fashion that the lower portion of the outer casing 1 is swelled out into a predetermined depth to accommodate an inner lower casing 6 within the expanded water chamber 2, said lower casing comprising a vane wheel chamber 4 and a water discharging chamber 5 integrally formed with and above the vane wheel chamber 4.
However, the height of said vane wheel chamber 4 and said water discharging chamber 5 becomes relatively higher as compared with the single casing water meter, and the water pool 2a of a considerable volume is inevitably formed around the entire surroundings of said vane wheel chamber 4, thus substantially increasing the size of the water meter.
Furthermore, in operation of the above conventional double casing water meter, the water incoming from the inlet 1a provided on the outer casing 1 flows via said water chamber 2 and through the water inflowing holes 7 provided on the cylindrical wall 4a of said vane wheel chamber 4 into the vane wheel chamber 4 and further rises up into the discharging chamber 5, thereby turning the vane wheel 3. The water then passes through the water discharging holes 5a provided on the cylindrical wall of said water discharging chamber 5 and flows through the water passage 9 formed between the cylindrical wall 5b and the inside wall of said outer casing 1, finally being discharged through said outlet 1b of said outer casing 1.
Such complicated inflowing and outflowing paths will cause head loss, thereby increasing the loss of water pressure. Consequently, the maximum amount of the flowing water is decreased because water flows out from said outlet 1b under a reduced pressure.
In the above conventional double casing water meter, floating substances, such as fine sand particles and sludge contained in the flowing water, are raised from the bottom 4b of said vane wheel chamber 4 up to the level of said water discharging holes 5a to be discharged therethrough with much difficulty by the running force of the inflowing water and by the water whirl caused by the high speed rotation of said vane wheel 3.
However, if the floating substances are relatively heavier and greater, or when the vane wheel 3 rotates very slowly, said floating substances will settle to the bottom 4b of said vane wheel chamber 4, thereby hampering the rotation of said vane wheel 3, or said floating substances are deposited in the water passage 9, thereby obstructing the water flow therethrough, and as a result thereof, the water meters often fail to fulfill the measuring function and become out of order, which is thus well known through long experience. In the accompanying drawings, the reference number 10 designates the upper inner casing which is not described in this specification.
As described above, the lower portion of the outer casing 1 of the prior double casing water meter is swelled out to form a relative greater water chamber 2 with a sufficient size in width and depth in order to let the water flow smoothly into the vane wheel chamber 4 via the inflowing holes 7, thus increasing the volume and weight of the outer casing 1 and accordingly requiring more materials in proportion to its size, and causing a great head loss due to the complicated inflowing and outflowing paths, and frequently resulting in operational troubles due to the accumulated floating substances.